The invention relates generally to electrophotographic imaging members, such as layered photoreceptor structures, and processes for making and using the same. More particularly, the embodiments pertain to a photoreceptor that incorporates specific copolymers to facilitate electron transport across the undercoat layer of the photoreceptor device.
Electrophotographic imaging members, e.g., photoreceptors, typically include a photoconductive layer formed on an electrically conductive substrate. The photoconductive layer is an insulator in the substantial absence of light so that electric charges are retained on its surface. Upon exposure to light, charge is generated by the photoactive pigment, and under applied field charge moves through the photoreceptor and the charge is dissipated.
In electrophotography, also known as xerography, electrophotographic imaging or electrostatographic imaging, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. Charge generated by the photoactive pigment move under the force of the applied field. The movement of the charge through the photoreceptor selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image. This electrostatic latent image may then be developed to form a visible image by depositing oppositely charged particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The imaging process may be repeated many times with reusable imaging members.
An electrophotographic imaging member may be provided in a number of forms. For example, the imaging member may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. In addition, the imaging member may be layered. These layers can be in any order, and sometimes can be combined in a single or mixed layer.
Typical multilayered photoreceptors have at least two layers, and may include a substrate, a conductive layer, an optional charge blocking layer, an optional adhesive layer, a photogenerating layer (sometimes referred to as a “charge generation layer,” “charge generating layer,” or “charge generator layer”), a charge transport layer, an optional overcoat layer and, in some belt embodiments, an anticurl backing layer. In the multilayer configuration, the active layers of the photoreceptor are the charge generation layer (CGL) and the charge transport layer (CTL). Enhancement of charge transport across these layers provide better photoreceptor performance.
A suitable charge blocking layer is capable of forming an electronic barrier to hole transport between the adjacent photoconductive layer and the underlying conductive layer. The blocking layer may be applied by any suitable conventional technique such as spraying, dip coating, draw bar coating, gravure coating and the like. Generally, charge blocking layers for negatively charged photoreceptors allow electrons from the photoconductive layer of the imaging member to migrate toward and inject into the conductive layer. In various systems, the photoreceptor can be either negatively or positively charged which requires the development of suitable charge blocking layers. For example, in a negatively charged system the electron transporting functionality of binders included in undercoat layers will provide efficient injection and transportation of charge from the generator layer to the conductive ground plane by increasing the electron mobility in the bulk of the undercoat layer (UCL). Further, incorporation of such blocking layer materials helps reduce, and preferably substantially eliminates, the dark decay due to negative charging memory of the generator layer. These materials help reduce, and preferably substantially eliminate, dark decay by increasing the bulk electron transport in the undercoat layer and at the charge generator-undercoat layer interface. Reusability of the photoreceptors may be affected by substantial charge buildup that occurs as the materials are continually charged and discharged within a short time span. The significant buildup of charge due to the incomplete discharge of the imaging member may induce dielectric breakdown of the materials or of the layers resulting in print defects like charge deficient spots, or increased background development. Because the charge buildup affects the reusability of photoreceptors, incorporating materials that increase transport across the photoreceptor layers, enabling efficient and complete discharge, will lead to improved imaging members for high speed imaging applications.
Thus, as the demand for improved print quality in high speed xerographic reproduction increases, there is a need to better facilitate electron transport across photoreceptor layers to minimize or eliminate dark decay and residual voltage (Vr) due to the inability of charge to move efficiently through the imaging member.
The terms “charge blocking layer” and “blocking layer” are generally used interchangeably with the phrase “undercoat layer.”
Conventional photoreceptors and their materials are disclosed in Katayama et al., U.S. Pat. No. 5,489,496; Yashiki, U.S. Pat. No. 4,579,801; Yashiki, U.S. Pat. No. 4,518,669; Seki et al., U.S. Pat. No. 4,775,605; Kawahara, U.S. Pat. No. 5,656,407; Markovics et al., U.S. Pat. No. 5,641,599; Monbaliu et al., U.S. Pat. No. 5,344,734; Terrell et al., U.S. Pat. No. 5,721,080; and Yoshihara, U.S. Pat. No. 5,017,449, which are herein incorporated by reference.
More recent photoreceptors are disclosed in Fuller et al., U.S. Pat. No. 6,200,716; Maty et al., U.S. Pat. No. 6,180,309; and Dinh et al., U.S. Pat. No. 6,207,334, which are herein incorporate by reference.
Conventional undercoat layers are also disclosed in U.S. Pat. Nos. 4,464,450; 5,449,573; 5,385,796; 6,858,363; and Obinata et al, U.S. Pat. No. 5,928,824, which are herein incorporated by reference.